Morphmix / Tarzan

Morphmix and Tarzan are both fully distributed, peer to peer networks of
anonymizing proxies, allowing people to tunnel out through the low latency
mix network. Morphmix includes some very interesting collusion detection
algorithms and Sybil defenses, while Tarzan makes use of the scarcity of IP
addresses to accomplish the same. The two primary differences between
these systems and I2P are related to I2P's threat model
and their out-proxy design (as opposed to providing both sender and receiver
anonymity). There is source code available to both systems, but we are not aware
of their use outside of academic environments.

Mixminion / Mixmaster

Mixminion and Mixmaster are networks to support anonymous email against a very
powerful adversary.
High-latency messaging applications running on top of I2P
(for example Syndie or I2PBote)
may perhaps prove adequate to meet the threat
model of those adversaries, while running in parallel along side the needs of low latency users, to provide
a significantly larger anonymity set.
High-latency support within the I2P router itself may or may not be added in a distant future release.
It is too early to say if I2P will meet the needs of users requiring extreme protection for email.

As with Tor and Onion Routing,
both Mixminion and Mixmaster take the directory based approach as well.

JAP

JAP (Java Anonymous Proxy) is a network of mix cascades for anonymizing web requests,
and as such it has a few centralized nodes (participants in the cascade) that blend
and mix requests from clients through the sequence of nodes (the cascade) before
proxying out onto the web. The scope, threat model, and security is substantially
different from I2P, but for those who don't require significant anonymity but still
are not satisfied with an Anonymizer-like service, JAP is worth reviewing. One
caution to note is that anyone under the jurisdiction of the German courts may want
to take care, as the German Federal Bureau of Criminal Investigation (FBCI) has
successfully mounted an
attack
on the network. Even though the method of this attack was later found to be illegal
in the German courts, the fact that the data was successfully collected is the
concern. Courts change their minds based upon circumstance, and this is evidence that
if a government body or intelligence agency wanted to, they could gather the data, even
if it may be found inadmissible in some courts later)

MUTE / AntsP2P

Both of these systems work through the same basic
antnet routing, providing some degree of
anonymity based on the threat model of providing plausible deniability against a simple
non-colluding adversary. With the antnet routing, they first either do a random walk or a
broadcast search to find some peer with the data or identity desired, and then use a feedback
algorithm to optimize that found path. This works well for applications that merely want to know
what other people around them have to offer - "How are y'all doing" vs. "Hey Alice, how are you" -
you basically get a local cluster of nodes that can share files with and maintain some degree of
anonymity (though you don't have much control over who is in that group of peers).

However, the algorithm does not scale well at all - if the application wants to speak with a
particular peer it ends up doing a broadcast search or random walk (though if they are lucky enough
for that to succeed, the antnet routing should optimize that found connection). This means that
while these networks can work great at small scales, they are not suitable for large networks where
someone wants to get in touch with another specific peer. That does not mean that there is no
value in these systems, just that their applicability is limited to situations where their
particular issues can be addressed.